نشریه مهندسی منابع معدنی
سال سوم شماره 2 (تابستان 1397)

In last decades, phenomenological constitutive damage models were used by many researchers to study for brittle failure of rock materials. Most phenomenological constitutive damage models utilize the irreversible thermodynamic principles to take into account the damage processes in brittle rock materials. Since this type of damage model do not consider the actual physical phenomena in the damage process, the micromechanical damage models are often used to consider the actual physical mechanisms in micro-scales specially in nucleation and propagation of wing-cracks from pre-existing flaws tips. Frictional sliding on closed micro-cracks surfaces leads to inelastic deformation and wing-cracks nucleation from flaw tips. Because of the different distribution of size and orientation of microflows in the rock materials, under dynamical loading, all of the pre-existing micro-flaws in the rock are activated and propagated. The interaction of micro-cracks with other and coalescence of these micro-cracks play a key role in accumulation of damage and macro-scale fracture plane formation in the rock. The various homogenization schemes e.g. Mori-Tanaka, Self-consistent and Ponte-Castandea were applied for calculation of equivalent mechanical parameters of materials. In this study, the Self-consistent scheme (SCS) was used for homogenization of rock sample under uniaxial dynamic compressive loading. The developed model was programmed and used as a separate and new constitutive model in the commercial finite difference software (FLAC).The dynamic compressive test of a brittle rock was simulated numerically and the stress-strain curves under dynamic loading were simulated and compared with one another. The proposed model predicts a macroscopic stress-strain relation and a peak stress (the materials compressive strength) with an associated transition strain rate beyond which the compressive strength of the material becomes highly strain rate sensitive. The results also show that as the strain rate increases, the peak strength increases and the damage evolution becomes slower.

Due to the population growth and the increasing demand for the construction of the infrastructure necessary for comfortable and fast transportation, tunneling has become especially important. Tunneling in urban areas by passing underneath several buildings causes subsidence due to stress relief and development of elastic and plastic deformations. If these subsidences are not controlled, the structures on the ground will be seriously damaged. Thus, proper estimation of subsidence is an important task when doing tunneling feasibility in urban areas. Nowadays, several methods are used for tunnel analysis and design and for urban tunnels, which excavated in shallow and soft grounds, the best way is using numerical methods. The study of excavation impact on stress distribution around tunnels as well as the study of ground surface subsidence in soft grounds are extremely important and should be deeply taken into account. This research addressed the 2D modeling of Modarres Tunnel of Arash-Esfandiyar-Niyayesh Tunnel Project by PLAXIS software. This tunnel is located in The Third Region of Tehran Municipality. The subsidences were determined through numerical modeling by hardening soil behavioral model, and, then, were compared to the results of the modeling by Mohr-Coulomb behavioral model. it was concluded that the excavation of Modarres tunnel, considering the modeling results and comparing them to the monitoring data, could be done in a controlled and safe manner by using NATM sequential excavation method and by utilizing the soil reinforcement elements such as fore-poling, nailing and micro-piles, and this experience should be used in similar tunneling sections. Furthermore, the use of hardening soil model was more appropriated for modeling the tunnel in the coarse-grained soil in Tehran which had the same conditions as this tunnel, than the Mohr-Coulomb model. The maximum subsidence in the modeling with the hardening soils model and the Mohr Coulomb model was 23.37 mm and 27.04 mm, respectively.

geomechanical properties of rock mass is a prerequisite for method selection in caving underground mining. Cavability index of rock mass is a key parameter in selecting those methods. , Some practical methods have been presented based on engineering rock mass classifications for the assessment of this index. Laubscher approach based on MRMR and Hydraulic Radius of undercut was one of acceptable methods in cavability assessment. In this study, geomechanical properties of rock mass which are influential on cavability were modeled by geostatistical tools based on surface and under surface data gained. Cavability of rock mass was estimated based on Laubscher approach by a model with 25×25×25 m blocks. Moreover, according to Laubscher Cavability Chart, the required equations were defined to assess this according to the classification of rock mass in mining projects and HR was obtained . in this study, Anomaly XII Sechahoon Mine data was investigated as case study and the associated cavability was estimated by geostatistical modelling. The results for HR=12.5 demonstrate that more than 80% of blocks adequately fall in thecavability condition while the rest of blocks fall in transition condition. Therefore this case study presents suitable cavability since the first step in mining method selection has been suggested for caving underground mining.